In ultrafast optics laboratories it is often desirable to measure the spatial or temporal profile of ultrashort pulses. In some situations, the temporal behavior of the pulse can depend on spatial coordinates, and separate spatial and temporal measurements are insufficient in order to obtain the desired profile, and complete spatio-temporal dependence of the pulse is needed. For example, a pulse can be contaminated by spatio-temporal distortions, such as spatial chirp, pulse-front tilt, or angular dispersion, which limit the performance of an ultrafast system such as might be the case, for example, with amplified or focused pulses. Alternatively, the pulse may have been used to excite or probe complex media with time-varying spatial structure. Indeed, spatio-temporal distortions are quite common, and only very carefully and precisely aligned pulses can be considered to be free of such distortions. Unfortunately, such precisely aligned pulses are generally obtained at significant cost and effort.
Also, there are situations in which the pulse may or may not have spatio-temporal distortions, but instead may simply be complex in time.